Powered sheave for node deployment and retrieval

ABSTRACT

A method and apparatus for deploying a plurality of seismic sensor units into a water column is described. The method includes providing a length of flexible cable from a cable storage device disposed on a vessel to a powered sheave, the cable having a plurality of spaced apart attachment points, routing the cable from the powered sheave to pass adjacent a workstation disposed on the vessel, deploying a free end of the cable into the water column while increasing the motion of the vessel to a first speed, operating the vessel at the first speed while providing a deployment rate of the cable at a second speed, the second speed being greater than the first speed, decreasing the second speed of the cable as an attachment point approaches the work station, and attaching at least one of the plurality of seismic sensor units to the attachment point at the workstation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to seismic exploration in marineenvironments.

2. Description of the Related Art

Seismic exploration operations generally utilize a seismic energy sourceto generate an acoustic signal that propagates into the earth. Theacoustic signal is partially reflected by subsurface seismic reflectorsin the earth, which may include interfaces between subsurface lithologicor fluid layers that may be characterized by different elasticproperties. The reflected signals are detected and recorded by seismicreceiver units located at or near the surface of the earth, therebygenerating a seismic survey of the subsurface. The recorded signals, orseismic energy data, can then be processed to yield information relatingto the lithologic subsurface formations, identifying such features, as,for example, lithologic subsurface formation boundaries.

Generally, the method for detection and recording of seismic signals issimilar on land and in marine environments; however, marine environmentspresent unique challenges due to the body of water overlaying theearth's surface. Seismic exploration operations in marine environmentsare typically conducted from the deck of one or more seismic explorationvessels, such as floating platforms or ships. The seismic explorationvessels typically provide storage and transportation for a plurality ofseismic receiver units and associated operational equipment. Seismicexploration in deep water typically uses seismic sensor units deployedfrom the deck of the seismic exploration vessel to be placed on or nearthe seabed. The seismic sensor units are typically coupled to a rope orcable that is placed in the water and allowed to fall through a watercolumn to the seabed. These seismic sensor units are part of systemstypically referred to as Ocean Bottom Cabling (OBC) or Ocean BottomSeismometer (OBS) systems, wherein data from a seismic survey may bereceived.

When performing a seismic survey in marine environments, a specific areaof the seabed is intended to be explored. Generally, a plurality ofseismic sensor units are coupled to a cable and deployed from adeployment vessel to form an array or grid of seismic sensor units onthe seabed. Typically, the accuracy of the seismic survey depends uponcontrolled placement of the sensor units on the seabed. The placement ofthe seismic sensor units deployed in this manner may be affected by manyfactors, some of which include position of the deployment vessel in thewater, wind speed, speed of the deployment vessel, and underwatercurrents caused by naturally occurring current flows and/or turbulencegenerated by the deployment vessel, among other factors.

Conventional deployment methods typically utilize variations in thespeed of the deployment vessel to control the deployment of the cable,which can lead to inconsistent deployment of the cable and inconsistentplacement of seismic sensor units. For example, if the deployment speedof the vessel is not controlled accurately or responsively, the cabledeployment may be erratic, which may cause seismic sensor unit placementinconsistencies. As an example, slack may build up in the cable betweenthe vessel and one or more seismic sensor units that have not fallen tothe seabed, which may make the towed cable susceptible to drift bycurrents. Another example includes slack build-up in the cable betweenseismic sensor units. Yet another example includes dragging of theseismic sensor units along the seabed. All of these examples can lead tounintended drift or movement of the seismic sensor units, possiblyplacing them outside of the intended areas to be tested.

Thus, there exists a need for an improved method and apparatus fordeploying seismic sensor units to be placed on a seabed from a seismicexploration vessel.

SUMMARY OF THE INVENTION

In one embodiment, a method for deploying a plurality of seismic sensorunits into a water column is described. The method includes providing alength of flexible cable from a cable storage device disposed on avessel to a cable handling device, routing the cable to pass adjacent aworkstation disposed on the vessel, deploying a free end of the cableinto the water column while increasing the motion of the vessel to afirst speed, varying the deployment rate of the cable by adjusting therotational speed of the cable handling device while maintaining themotion of the vessel at the first speed, and attaching at least one ofthe plurality of seismic sensor units to the cable as the cable passesthe workstation.

In another embodiment, a method for deploying a plurality of seismicsensor units into a water column is described. The method includesproviding a cable handling device, coupled to a marine vessel,comprising a powered sheave and an idler sheave, the powered sheavehaving a first cable contact area and the idler sheave having a secondcable contact area opposing the first cable contact area, coupling alength of a flexible cable to the cable handling device in a route tocontact the first cable contact area and second cable contact area tomaintain a frictional force applied to a section of the flexible cable,routing the cable from the powered sheave to the stern of the vessel topass across a workstation, deploying a free end of the cable into thewater column while increasing the motion of the vessel to a first speed,providing a deployment rate of the cable to a second speed by adjustingthe rotational speed of the powered sheave, and attaching at least oneof the plurality of seismic sensor units to one of a plurality ofattachment points disposed on the cable as the cable passes theworkstation.

In another embodiment, a method for deploying a plurality of seismicsensor units into a water column is described. The method includesproviding a length of flexible cable from a cable storage devicedisposed on a vessel to a powered sheave, the cable having a pluralityof spaced apart attachment points, routing the cable from the poweredsheave to pass adjacent a workstation disposed on the vessel, deployinga free end of the cable into the water column while increasing themotion of the vessel to a first speed, operating the vessel at the firstspeed while providing a deployment rate of the cable at a second speed,the second speed being greater than the first speed, decreasing thesecond speed of the cable as an attachment point approaches the workstation, and attaching at least one of the plurality of seismic sensorunits to the attachment point at the workstation.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a perspective view of one embodiment of a node deploymentoperation.

FIG. 1B is a perspective view of one embodiment a retrieval operation.

FIG. 2 is an operational view of a seismic vessel on a body of water.

FIG. 3 is a schematic top view of a portion of a vessel having oneembodiment of a node storage and handling system.

FIG. 4A is a schematic side view of a portion of the node storage andhandling system shown in FIG. 3.

FIG. 4B is a schematic front view of the conveyor section of FIG. 4Ahaving one embodiment of a node servicing system.

FIG. 4C is a schematic side view of the cable handling system 210 shownin FIG. 3.

FIG. 5 is a top plan view of a portion of a vessel having anotherembodiment of a node storage and handling system.

FIG. 6 is a flowchart showing one embodiment of a deployment method.

FIG. 7 is a flow chart showing one embodiment of a retrieval method.

FIG. 8 is a perspective view of one embodiment of a cable handler.

FIG. 9 is a cross-sectional view of the cable handler of FIG. 8.

FIG. 10 is a flowchart showing one embodiment of a deployment method.

FIG. 11 is a flowchart showing another embodiment of a deploymentmethod.

FIG. 12 shows one embodiment of a fall pattern for a mainline cable.

FIG. 13 shows another embodiment of a fall pattern for a mainline cable.

FIG. 14 shows another embodiment of a fall pattern for a mainline cable.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Embodiments described herein generally provide methods and apparatus fororganization and safety of a marine vessel used in a seismic explorationoperation, although certain embodiments of the apparatus and methods maybe extended to other operations and industries, such as land basedmaterials handling operations. In some embodiments, an apparatus andmethod of handling, storage, deployment and/or retrieval of one or moreseismic sensors in or on a body of water is described. These seismicsensors may include seismic devices used in Ocean Bottom Cabling (OBC)or Ocean Bottom Seismometer (OBS) systems. The seismic devices may beinterconnected electronically, such as by wires or wirelesscommunication links, or may be discrete units where data is storedand/or recorded. In some embodiments, the seismic devices may bedetachably coupled to a length of rope or cable during deployment and/orretrieval operations. One type of seismic device includes aself-contained ocean bottom sensor unit, sometimes referred to as aSeafloor Seismic Recorder (SSR), which is configured to receive, record,and store seismic data. SSR's are typically detachably coupled to alength of rope or cable during deployment and retrieval operations. Anexample of a self-contained ocean bottom sensor unit is described inFIGS. 1-8 of U.S. Pat. No. 7,310,287, which issued Dec. 18, 2007, and isincorporated herein by reference. Although embodiments described hereinare exemplarily described with seismic sensor units that may bedetachably coupled to a rope or cable during deployment and/or retrievaloperations, the handling methods and apparatus may be used with otherdevices and in other industries. The seismic sensor units as describedherein may be used in OBS systems or OBC systems and are collectivelyreferred to herein after as nodes for ease of description.

FIG. 1A is a perspective view of one embodiment of a node deploymentoperation 100A. A vessel 105 is positioned on a body of water 108 todeploy nodes 110 from a backdeck 115 of the vessel 105 into a watercolumn 120, although other deployment locations from the vessel 105 maybe used. Examples of other deployment locations include the bow or sideof the vessel. The power and/or momentum of the vessel 105 may be usedto assist in paying out a cable 125A and 125B to which nodes 110 areattached. In this example, a plurality of nodes 110 are tethered to anon-rigid cable 125A to form a mainline cable 125B that is deployed intothe water column 120 using the power and/or momentum of the vessel 105.The mainline cable 125B sinks to a resting position on or near a floor130 of the water column 120. In one embodiment, a free end 135 of themainline cable 125B is attached to an anchor device 140 such that thecable 125A may be spooled, paid-out, or otherwise deployed from thebackdeck 115 of the vessel 105. The free end 135 may also be coupled toa flotation or buoyancy device 165 that may be selectively actuated toassist in locating and/or retrieving the cable 125 after the survey iscompleted.

As the cable 125A is routed over the backdeck 115, the cable 125A passesa workstation 145, as shown in FIG. 2, where nodes 110 may be attachedto the cable 125A to form the mainline cable 125B. In one example, thenodes 110 are attached individually and sequentially to the cable 125Aby personnel on the vessel 105, or suitably mechanically attached to thecable 125A, as the cable 125A passes the workstation 145. Once themainline cable 125B is positioned on or near the floor 130, a seismicsurvey may be performed. Upon completion of the seismic survey, themainline cable 125B may be retrieved from the water column 120. In oneembodiment, the buoyancy device 165 is actuated to bring a free end 135near the surface of the water column 120 where personnel on the vessel105 may acquire and secure the mainline cable 125B.

FIG. 1B is a perspective view of one embodiment a retrieval operation100B. The vessel 105 has a trailing end 150 and a leading end 155. Inthis example, the mainline cable 125B is retrieved over the trailing end150, typically the stern, of the vessel 105 as the leading end 155,typically the bow, of the vessel travels over the mainline cable 125Bdisposed on the floor 130 in a general direction toward the anchordevice 140. The “over the stern” retrieval method uses the water column120 to reduce dragging, excess tensioning and/or pulling of the cable125B across the floor 130 as the cable 125B is retrieved.

In one embodiment, the mainline cable 125B is retrieved using a cablehandler 160, which may be a winch or a power block, a powered reel,pulley or sheave device. During retrieval, the mainline cable 125B isrouted across a portion of the workstation 145 of the vessel 105. As themainline cable 125B passes by the workstation 145, nodes 110 aredetached from the cable 125A. In one embodiment, the nodes 110 aredetached by personnel on the vessel 105 or suitable mechanical device ator near the workstation 145. After the nodes 110 are detached, the nodes110 are stowed in a storage device and serviced if necessary. In oneembodiment, the nodes 110 are routed to a storage device where data iscollected, batteries are charged, and general servicing, such as qualitycontrol and/or maintenance may be performed.

FIG. 2 is an operational view of a seismic vessel 105 on a body of water108 having one embodiment of a node storage and handling system 200. Thenode storage and handling system 200 includes a cable handling system210 and a storage device 220 coupled by a staging portion 230. The nodestorage and handling system 200 facilitates storage of a plurality ofnodes 110 while providing automated routing of nodes 110 duringhandling, such as during a deployment or retrieval operation.

The storage device 220 includes a conveyor system 221 to store and/ortransfer the plurality of nodes 110. In this example, the conveyorsystem 221 is linear and includes three stacked and independentlyactuatable conveyor sections 222A, 222B and 222C at different heightsabove the backdeck 115, although any number of conveyors may be used. Inother embodiments, the conveyor system 221 may be non-linear, such as anarcuate conveyor system, for example, a carousel-type conveyor system.Each of the conveyor sections 222A-222C include a movable upper surface236 adapted to support a plurality of nodes 110. In one embodiment, eachconveyor section 222A-222C includes a rotatable belt or mesh adapted tosupport and transfer the nodes 110. The rotatable belt or mesh on eachof the conveyor sections 222A-222C is coupled to a drive configured tomove the belt or mesh and transfer the nodes 110. The storage device 220also includes a node servicing system 223, which may include a datain/data out system and a node recharging system. In one example, thenode servicing system 223 comprises a plurality of wires or cables (notshown) which detachably couple to one or more of the plurality of nodes110.

The cable handling system 210 includes a portion of a workstation 145where nodes 110 may be attached or detached from the cable 125A, 125B.The cable handling system 210 also includes a cable handler 160 and acable storage device 213. The cable handler 160 may be a winch, apowered roller, spool, or sheave adapted to retrieve or deploy the cable125A and/or 125B. The cable storage device 213 may include a cablestorage area or bin located in or on the backdeck 115 and may alsoinclude a cable handling mechanism, such as a spool, a cable puller, acable squirter, or other device adapted to lay or pick-up cable 125Afrom the cable storage area. The cable 125A is routed by the cablehandler 160 to or from the cable storage device 213 and a ramp 214coupled to the trailing end 150, or stern, of the vessel 105. The cable125A (or 125B) is routed across the workstation 145, which includes aportion of the ramp 214 and a portion of the staging portion 230. In oneembodiment, the cable handler 160 includes a powered pinch sheave 211and an idler 212 such that the cable 125A is routed in an “S” fashionthrough the cable handler 160 as shown in FIG. 8.

The storage device 220 and the cable handling system 210 are coupledwith the staging portion 230 such that nodes 110 may be provided fromthe cable handling system 210 to the storage device 220, or vice versa.The staging portion 230 includes at least a portion of the workstation145 so personnel may attach or detach nodes 110 from the cable 125A (or125B). The staging portion 230 also includes a stationary conveyor 231coupled between at least a portion of the ramp 214 at one end, andcoupled to or adjacent a movable conveyor 232. Each of the conveyors 231and 232 include a movable upper surface 236 adapted to support one ormore nodes 110. Each of the conveyors 231 and 232 may include arotatable belt or mesh conveyor having an upper surface 236 adapted tosupport one or more nodes 110. The rotatable belt or mesh on each of theconveyors 231 and 232 are coupled to a drive configured to move the beltor mesh and transfer the nodes 110.

The movable conveyor 232 has a first end 233 that substantially matchesa height of the upper surface 236 of the stationary conveyor 231 and asecond end 234 that may be raised or lowered relative to a second end225 of the conveyor system 221. The interface between the stationaryconveyor 231 and the movable conveyor 232 may include matchingrespective heights such that nodes 110 may be transported between theconveyors 231, 232 in a seamless fashion. The second end 234 may beraised or lowered to substantially match the height of one of theconveyor sections 222A-222C in a manner that provides a travel path fromeach of the conveyor sections 222A-222C to the stationary conveyor 231,and vice versa.

In a deployment operation, which is further detailed in FIGS. 6 and 10,the cable 125A may be coupled to the cable handler 160 and routed topass near the workstation 145. Nodes 110 may be routed from one of theconveyor sections 222A-222C across the movable conveyor 232 and thestationary conveyor 231 to the workstation 145. At the workstation,personnel may attach the nodes to the cable 125A at node attachmentpoints 245 disposed on the cable 125A. In one embodiment, personnel ator near the workstation 145 may attach a rope, tether, chain or cable,such as a lanyard 240, to the cable 125A. The lanyard 240 may beflexible and adapted to couple at one end to a node 110 and at anotherend to the cable 125A at the node attachment point 245. In oneembodiment, the lanyard 240 is a non-conductive rope, chain or cable.The lanyard 240 may be tied to each of the node attachment point 245 andnode 110, fastened with clamp devices, such as D-rings, shackles, clipsor carabineer clamps, or other fastener.

As the cable 125A is deployed from the vessel 105, the nodes 110 andcable 125A fall through the water column 120 to rest at or near thefloor 130, as shown as the mainline cable 125B in FIG. 1A. Thisoperation continues until the cable 125A is paid out to a second endwhere an anchor device and/or flotation device is coupled to a free end135 described in FIG. 1A. Additional lengths of cable 125A may becoupled to the cable handler 160, and paid out similarly as describedabove, until an array of mainline cables 125B is laid out on the floor130. Once one or more mainline cables 125B are positioned on the floor130, a seismic survey may be performed.

A retrieval operation may be performed in a generally reverse mannerafter the seismic survey is performed, which is further illustrated atFIG. 7. One of the free ends of the cable 125B is interfaced with thecable handler 160. As the cable 125B is hauled out of the water, andonto the vessel 105, the cable 125B passes over the workstation 145where personnel detach the nodes 110 and/or lanyards 240 from the cable125B. Nodes 110 may be routed to one of the conveyor sections 222A-222Cby the stationary conveyor 231 and movable conveyor 232 for storage,data retrieval, charging and/or maintenance.

FIG. 3 is a schematic plan view of a portion of a vessel 105 having oneembodiment of a node storage and handling system 200. The node storageand handling system 200 includes a cable handling system 210 and astorage device 220 coupled by a staging portion 230. Each of theconveyors 231, 232, and each conveyor section disposed in the conveyorsystem 221 (only section 222A is shown) includes a drive system 320 thatmay be a reversible, variable speed motor that provides bidirectionaland controlled movement of the conveyors 222A-222C, 231, and 232 and thenodes 110 thereon. As the stationary conveyor 231 and movable conveyor232 are coupled together at a substantially normal orientation, adiverter 325 may be coupled above an upper surface 236 of the stationaryconveyor 231. The diverter 325 is configured to turn or reorient nodes110 at the interface between the movable conveyor 232 and stationaryconveyor 231 and may be coupled in a manner that does not interfere withthe movement of the upper surface 236 of the stationary conveyor 231 orthe movable conveyor 232. In one embodiment, the diverter 325 is astraight or curved plate disposed above a movable upper surface 236 ofthe stationary conveyor 231. In one specific embodiment, the diverter325 is disposed above the movable upper surface 236 at about a 45° angleto the travel direction of the movable upper surface 236.

The backdeck 115 of the vessel 105 may also include one or moreworkstations 345A and 345B where personnel may handle nodes along acable path 300 (shown as a dashed line) between a portion of the ramp214 and cable handler 160. Each of the workstations 345A, 345B areadjacent a tray 305 that lies under or on the cable path 300. Eachworkstation 345A, 345B includes a portion of the backdeck 115 sufficientfor at least one person to easily and safely access the cable and/ornodes 110. At least one of the workstations 345A, 345B may include acontroller 310 adapted to control one or more functions of the nodestorage and handling system 200. For example, the controller 310 mayallow personnel to control retrieval or deployment speed of the cablehandler 160, rotational speeds of one or both of the conveyors 231, 232,a height of the second end 234 of the movable conveyor 232, speeds ofindividual conveyor sections on the conveyor system 221, andcombinations thereof.

The cable handling system 210 includes a cable storage device 213 thatincludes a cable puller 380 adjacent a cable bin 332. In one embodiment,the cable puller 380 is movably coupled to a frame 330 in a cantileverfashion. The cable bin 332 includes at least two rails 350 and 355adapted to separate an area from the backdeck 115 for cable storage. Thecable puller 380 may be coupled to a trolley 334 disposed on the frame330. The trolley 334 and cable puller 380 are adapted to move relativeto the cable bin 332 to deposit or feed the cable 125A to or from thecable bin 332 in an orderly fashion. For example, during a deploymentoperation, the cable puller 380 and trolley 334 may initially be near afirst end 336 of the cable bin 332 and move toward a second end 338 topick up the cable 125A in the bin 332 in a stepwise and orderly fashion.In a retrieval operation, the cable puller 380 and trolley 334 mayinitially start at the second end 338 and move toward the first end 336to lay the cable 125A in the bin 332 in a stepwise and orderly fashion.

FIG. 4A is a schematic top view of a portion of the node storage andhandling system 200 shown in FIG. 3. In one embodiment, at least aportion of the staging portion 230 includes a movable conveyor 232having a first end 233 and a second end 234. The first end 233 includesa height that substantially equals the height of the stationary conveyor231 while the second end 234 may move up or down relative to theindividual conveyor sections 222A-222C. As an example, the second end234 of the movable conveyor 232 may be raised to transfer nodes 110 toor from conveyor section 222A, as shown in phantom. An actuator 400,which may be a hydraulic cylinder, a pneumatic cylinder, a lead screw orother linear actuator, may be coupled to the movable conveyor 232 tocontrol vertical positioning of the second end 234. In one embodiment,the first end 233 includes a pivot point 402. The pivot point 402maintains the height of the upper surface 236 of the movable conveyor232 with the height of the upper surface 236 of the stationary conveyor231 while allowing the second end 234 to move up and down.

Each of the conveyor sections 222A-222C may provide storage for andtransport of a plurality of nodes 110. In one embodiment, each conveyorsection 222A-222C may be configured to store and transport up to about16 nodes 110 per section, in another embodiment, about 32 nodes may bestored and transported by each section 222A-222C. In another example,each conveyor section 222A-222C may be configured to store and transportup to about 200 nodes per section. The conveyor system 221 may also beof a suitable length or height that is commiserate with the availabledeck space of the vessel 105, and may be coupled with additionalconveyor systems similar to conveyor system 221. For example, theconveyor system 221 includes a first end 224 opposite the second end225, and a second conveyor system (not shown) may be placed adjacent thefirst end 224. In this example, conveyor sections 222A-222C may bepositioned adjacent other conveyor sections (not shown) such that agreater storage capacity for nodes 110 may be provided.

FIG. 4B is a schematic front view of a conveyor section 221 having oneembodiment of a node servicing system 223, which may include a datain/data out system, such as a digital data collection system (DDCS), anda node recharging system. The node servicing system 223 includes aplurality of leads 405 adapted to couple to nodes 110. Each lead 405 maybe a wire or cable adapted to transmit data to, or receive data from, acontroller, and/or be coupled to a power source to recharge therespective node 110 it is coupled to.

FIG. 4C is a schematic side view of the cable handling system 210 shownin FIG. 3. As explained above with reference to FIG. 3, the cablestorage device 213 may include a frame 330 that is adjacent a cable bin332 and a cable puller 380 is movably coupled to the frame 330 in acantilever fashion. In another embodiment, the cable puller 380 may bedirectly coupled to rails 350 and 355 (only one is shown in this view)such that the frame 330 and trolley 334 are not needed. For example, thecable puller 380 may include a drive system 410 adapted to move thecable puller 380 relative to the ends 336 and 338 of the rails 350, 355.In this manner, space on the backdeck 115 required for the cablehandling system 210 may be reduced.

FIG. 5 is a top plan view of a portion of a vessel 105 having anotherembodiment of a node storage and handling system 200. In thisembodiment, conveyor systems 521A-521D are coupled in an end to endmanner to extend the node storage area of the storage device 220. Eachconveyor system 521A-521D may be similar to conveyor system 221 asdescribed above. For example, each conveyor system 521A-521D may includethree vertically stacked conveyors sections similar to conveyor sections222A-222C, or a suitable number of stacked conveyors sections, such astwo or more stacked conveyors sections. In this embodiment, the conveyorsystems 521A-521D are arranged in rows 505A-505F that are substantiallyparallel to the cable path. Two stationary conveyors 231 are providedalong two sides of the ramp 214 to facilitate transfer of nodes 110 to aplurality of movable conveyors 532. The movable conveyors 532 may besimilar to the movable conveyors 232 described above, and are alignedwith each row 505A-505F. Each row 505A-505F may facilitate storage andtransfer of a plurality of nodes 110 and rows may be added or subtractedbased on the width of the backdeck 115. In one embodiment, each row505A-505F facilitates storage and transfer of about 200 nodes 110, perrow. In this embodiment, the vessel 105 may store about 1200 nodes 110.A secondary cable storage area 513 may also be added to the vessel 105to facilitate storage of additional cables 125A.

FIG. 6 is a flowchart showing one embodiment of a deployment method 600.At 610, a cable 125A having a plurality of node attachment points 245 iscoupled to a cable handler 160, which may comprise routing a free end ofthe cable 125A in an “S” fashion through the cable handler 160 as shownin FIG. 8. The free end 135 of the cable 125A may be coupled to ananchor device 140 and/or flotation device 165 (FIGS. 1A and 1B) anddisposed into the water over the trailing end 150 of the vessel 105. At620, the cable 125A is paid out or controllably released by the cablehandler 160 to pass over a portion of or adjacent to the workstation 145and into the body of water 108. At 630, nodes 110 are provided to theworkstation 145 from the node storage area 220 along a moving surface.In one embodiment, the moving surface includes multiple conveyor beltsdisposed on each of the conveyor sections 222A-222C, the stationaryconveyor 231 and movable conveyor 232. In a specific embodiment, nodes110 travel from one of the conveyor sections 222A-222C to the stationaryconveyor 231 across the movable conveyor 232 to the workstation 145. At640, individual nodes 110 are attached to the cable 125A as the cable125A passes the workstation 145. In one embodiment, personnel at or nearthe workstation 145 may attach a lanyard 240 to the cable 125A. Thelanyard 240 may be tied or otherwise fastened to each of the nodeattachment point 245 and node 110. The operation described at 640 maycontinue until the cable 125B is released by the cable handler 160 to asecond end where another anchor device 140 and/or flotation device 165may be coupled thereto. The cable 125B may be released from the vessel105 and allowed to rest at or near the floor 130 of the water column120. Alternatively, a free end 135 of another length of cable 125A maybe attached to the second end of the cable 125B in order to lengthen themainline cable 125B. In this embodiment, the method may repeat 610-640to attach and deploy additional nodes 110 on a second length of cable125A.

At 650, a determination may be made based on the area of the array to belaid at or near the floor 130 of the water column 120. If additionalmainline cables 125B are needed for the array, additional lengths ofcable 125A may be provided and steps 610-640 are repeated to provideadditional mainline cables 125B. If additional cables 125B are notneeded for the array, and one or more mainline cables 125B arepositioned on the floor 130 to define the array, a seismic survey may beperformed at 660. At 660, a seismic energy source may be actuated toprovide one or more acoustic signals which is propagated into theearth's surface. The reflected signals are detected and recorded by thenodes 110 in the array.

FIG. 7 is a flow chart illustrating one embodiment of a retrieval method700. After a seismic survey has been performed, and/or a determinationhas been made to retrieve the cable 125B from the floor 130, a free end135 of the cable may be retrieved from the water at 710. In one example,a buoyancy device 165 (FIGS. 1A and 1B) may be activated to raise thefree end 135 of the cable 125B. One or both of the buoyancy device 165and cable 125B may be grabbed or secured by personnel on the vessel 105.720 describes attaching the free end 135 to the cable handler 160 in amanner that allows the cable 125B to pass at or near the workstation 145once the cable 125B is secured by personnel. At 730 nodes are detachedfrom the cable 125B as the cable passes the workstation 145. In oneembodiment, personnel at the workstation 145 detach the lanyards 240from the node attachment points 245 on the cable 125B. At 740 detachednodes 110 are transferred to the node storage area 220 along a movingsurface 236. In one embodiment, the moving surface 236 includes multipleconveyor belts disposed on each of the stationary conveyor 231, themovable conveyor 232 and each conveyor section 222A-222C. In a specificembodiment, nodes 110 travel from the workstation 145 to the stationaryconveyor 231 and across the movable conveyor 232 to one of the conveyorsections 222A-222C.

After nodes 110 have been transferred to the conveyor sections222A-222C, the node servicing system 223 may be interfaced with at leasta portion of the retrieved nodes 110. Data may be retrieved and/or thenodes may be recharged and otherwise readied for long-term storage or asubsequent deployment operation.

FIG. 8 is a perspective view of one embodiment of a cable handler 160.In this embodiment, the cable handler 160 includes a powered pinchsheave 211 and an idler pulley 212. The powered pinch sheave 211includes a hub 805 coupled to two side members 810A, 810B by a pluralityof bolts 815. The side members 810A, 810B define a sheave well 930A,around an outer circumference, that is adapted to receive a cable 125A.The idler pulley 212 may also include side members to define a sheavewell 930B. The hub 805 may be a drive gear, such as a planetaryreduction gear, coupled to a drive motor 910, shown in FIG. 9, adaptedto provide a torque to the sheave 211. A plurality of rotatable guidemembers 820 may be disposed along the circumference of one or both ofthe sheave 211 and idler pulley 212. The guide members 820 areconfigured to provide a compressive force against each of the sheave 211and the idler pulley 212. Each guide member 820 may be a compliantcircular body that is adapted to contact at least a portion of thecircumference of the sheave 211 and/or the idler pulley 212. Each guidemember 820 is adapted to rotate relative to the sheave 211 and/or theidler pulley 212. Each guide member 820 may be actuated away from thesheave 211 and the idler pulley 212 to allow personnel to route thecable 125A through the cable handler 160. Additionally, a guard 830,only partially shown, may be used in combination or in place of theguide members 820 to reduce the possibility of the cable 125A fromfalling out of the sheave well 930A. The idler pulley 212 may alsoinclude a guard (not shown).

FIG. 9 is a cross-sectional view of the cable handler 160 of FIG. 8. Thepowered pinch sheave 211 includes two side members 810A and 810B coupledto the hub 805. Each of the side members 810A, 810B are spaced to definea radial gap 905 that receives at least a portion of the cable 125A. Theradial gap 905 is configured to provide additional friction to the cable125A as it passes around the sheave 211. The hub 805 is coupled to adrive motor 910 adapted to rotate the sheave 211. The drive motor 910may be hydraulically powered, electrically powered, pneumaticallypowered, or mechanically powered, such as a by a shaft coupled to anengine. The drive motor 910 is adapted to provide variable andreversible rotation to the sheave 211. The drive motor 910 may becoupled to a mounting portion 915 to stabilize the drive motor 910. Inthis embodiment, the drive motor 910 is a hydraulic motor coupled torespective valves 918 by hoses 920. In one embodiment, the valves 918may be coupled to a controller to control the speed and/or rotation ofthe sheave 211.

In one embodiment, each of the powered pinch sheave 211 and the idlerpulley 212 include respective circumferential sheave wells, shown as930A and 930B (930B is shown in phantom). Each sheave well 930A, 930B issized to receive the cable 125A and a portion of a guide member 820(FIG. 8). In one embodiment, the diameter of the sheave well 930A thatthe cable 125A is adapted to contact is about 32 inches. The poweredpinch sheave 211 and the idler pulley 212 are positioned such that thecable 125A is routed in an “S” fashion as shown in FIG. 8.

FIG. 10 depicts a method 1000 for deploying a cable, which will bedescribed in reference to FIGS. 1A and 1B, unless otherwise noted. Forease of understanding, a cable 125 will be described with FIGS. 10 and11. The cable 125 as described in FIGS. 10 and 11 may refer to a rope orcable with or without nodes attached. In one embodiment, the method 1000compensates for factors that may effect placement of the nodes 110 onthe floor 130 of the water column 120. The process starts at 1010, wherethe cable 125 is routed through the cable handler 160. In oneembodiment, the cable 125 may be routed as depicted in FIG. 8. At 1020,a free end 135 of the cable 125 is deployed into the water column 120.In one embodiment, the free end 135 of the cable 125 may include anattached node 110, a weight, such as an anchor device 140, and/orflotation device 165. At 1030, nodes 110 are attached to the cable 125as the cable 125 is being deployed into the water column 120.

After deployment of the free end 135, a plurality of deploymentparameters are assessed and monitored. The deployment parameters mayinclude a rotational speed of the pinch sheave 211 (FIGS. 8 and 9), atensional metric of the cable 125, a speed of the vessel 105, and aposition of the vessel 105 in the body of water 108. In one embodiment,the deployment parameters include factors that may be measured andcontrolled by personnel on the vessel 105. The deployment parameters mayalso include a placement plan of the nodes 110 on the floor 130 of thewater column 120. For example, the deployment parameters may include aspeed of the vessel in the water, a deployment speed of the cable,intervals between nodes 110 along the cable 125, among other factorsthat facilitate intended placement of the nodes 110 on the floor 130.

At 1040, a plurality of factors affecting deployment are monitoredduring deployment of the cable 125. Factors affecting deployment mayinclude a flow current within the water column 120, a wind speed and/ordirection, a metric indicative of drag of the cable 125 in the watercolumn 120 and/or along the floor 130, among other factors that mayaffect deployment and/or placement of the nodes 110. Flow currentswithin the water column 120 may be naturally occurring currents and/orcurrents generated by the vessel 105, currents generated by a propulsionsystem of the vessel 105, and combinations thereof. One or more of thefactors affecting deployment may be monitored by a controller (notshown) and/or observation devices (also not shown), such as a windmonitor, a current monitor, a global positioning system (GPS), a speedmonitor, force monitors and the like, attached to the cable handler 160and/or vessel 105. Monitoring of one or more of the factors affectingdeployment to maintain and/or adjust one or more deployment parametersas described herein facilitates a specific fall profile of the cable125, which is described below.

At 1050, a check is done to determine if any of the factors affectingdeployment has changed. In one embodiment, the check may be done bycomparing observations taken in previous time periods to observations ata later time period. If any of the factors affecting deployment havechanged then the method moves to 1060. At 1060, one or more deploymentparameters may be adjusted based on current or past observations. Onceone or more parameters are adjusted, the process again proceeds to 1040where factors affecting deployment are monitored, and then to 1050 wherethe factors affecting deployment are re-checked to see if any factorsaffecting deployment have changed. If any factors affecting deploymenthave not changed then the process proceeds to 1070. At 1070, a check isdone to see if a desired length of the cable 125 has been deployed. Ifnot, the process moves to 1080 where deployment of the cable iscontinued. After 1080, the process again moves back to 1040, which isdescribed above. If deployment is complete then the process moves to1090 and the process may end. If an array comprising more than onecables disposed on the floor 130 is desired, discrete additional cablesmay be coupled to the cable handler as described at 1010 and the processmay continue until all cables have been deployed.

FIG. 11 is a flowchart describing another embodiment of a deploymentmethod 1100, which will be described in reference to FIGS. 1A and 1B,unless otherwise noted. The method begins at 1110, where the cable 125is routed through a cable handler 160. While the method 1100 isdescribed using the cable handler 160, any device capable of un-spoolinga cable or rope in a controlled manner may be used. In one embodiment,the cable 125 may be routed through the cable handler 160 as depicted inFIG. 8. At 1120, a free end 135 of the cable 125 is deployed into thewater column 120. In one embodiment, the free end 135 of the cable 125may include an anchor device 140 and/or flotation device 165.

After the free end 135 of the cable 125 has been deployed, the vessel105 may be put into motion. In one embodiment, motion of the vessel 105is initiated after the anchor device 140 has reached the floor 130. Oncethe free end 135 has been placed on the floor 130 and/or the cable 125is otherwise suitably locationally placed in the water column 120 and/oron the floor 130, motion of the vessel 105 is increased. In oneembodiment, the motion of vessel 105 may be increased to a first speedas described at 1130. In one embodiment, the first speed is betweenabout 3 knots to about 5 knots.

During the increase in motion of the vessel 105, the cable 125 may beincreased and continuously released out of the vessel 105 into the watercolumn 120 while the vessel 105 speed is maintained. In one embodiment,the release rate or speed of the cable 125 may be varied while thevessel 105 speed is maintained. For example, the first speed of thevessel 105 may be maintained and the release of the cable may beincreased to a second speed. In one embodiment, the second speed isgreater than the first speed. In one example, the release of the cable125 is provided and controlled by the cable handler 160. In one example,the release rate of the cable 125 is controlled by the cable handler 160and the release rate is determined by the rotational speed of the cablehandler 160, specifically the rotational speed of the powered pinchsheave 211 (FIG. 8). In one embodiment, the rotational speed is variedbetween about 0 revolutions per minute (RPM) and about 100 RPM based ona diameter of the powered pinch sheave 211 of about 32 inches. Inanother embodiment, the cable 125 is released at a rate that equals thefirst speed of the vessel 105.

In one embodiment, the release rate of the cable 125 is faster than thefirst speed of the vessel 105 as described at 1140. In this embodiment,the release speed of the cable 125 is greater than the vessel speed. Forexample, the vessel speed may remain constant and the release speed ofthe cable is increased to provide slack in the cable 125. In thisembodiment, the cable 125 may be released at a rate that causes thecable to gather or accumulate at or near the surface of the water column120 adjacent the stern of the vessel 105. For example, the cable 125 isreleased at a rate or speed faster than the vessel speed, therebycreating slack within the cable 125 at or near the surface of the watercolumn 120. In one example, if the first speed of the vessel 105 ismaintained at about 3.5 knots, the release speed of the cable may beabout 90 RPM based on a diameter of the powered pinch sheave 211 ofabout 32 inches.

At 1150, the release rate or speed of the cable 125 is reduced while thevessel 105 speed is maintained. In one embodiment, the second speed ofthe cable 125 is reduced to facilitate attachment of a node 110 to thecable 125, as shown at 1160, while the first speed of the vessel 105 ismaintained. The decreased release rate may be between 0 RPM to about 10RPM based on a diameter of the powered pinch sheave 211 of about 32inches at the cable contact area, for example, between about 0 RPM toabout 2 RPM. Specifically, the release rate of the cable handler 160 isreduced as a node attachment point 245 (FIG. 2) nears the workstation145 (FIG. 2). In this embodiment, the vessel 105 speed is maintainedsuch that the accumulated slack in the cable 125 is depleted.

The first speed of the vessel 105 and the spacing of nodes 110 aredetermined so accumulated slack in the cable 125 from step 1140 isremoved. For example, the first speed of the vessel 105 is determinedand based at least partially on the spacing of the node attachmentpoints 245 so accumulated slack will be removed and a desired tensionwill be placed on the cable 125. In one embodiment, the first speed ofthe vessel 105 is such that the cable 125 disposed in the water column120 and/or nodes 110 disposed on the floor 130 is not caused to drag orbe pulled.

At 1170, the release rate or speed of the cable 125 is increased after anode 110 has been attached. In one embodiment, the release rate of thecable 125 may be returned to the second speed as described above whilethe first speed of the vessel 105 is maintained. The increase in therelease rate of the cable 125 may be based on instructions frompersonnel based on observing the slack in the cable 125. For example, anaudible and/or visible signal or instruction may be given from personnelobserving the deployment. For example, personnel may visually observethe tension in the cable 125 to provide a signal for increasing releasespeed of the cable 125. In another aspect, personnel may observedeployment parameters and/or factors affecting deployment to provide asignal for increasing the release speed of the cable 125. In anotheralternative, an audible and/or visible signal or instruction may beprovided from a controller that is pre-programmed based on the speed ofthe vessel 105 and spacing of node attachment points 245. In anotherembodiment, the controller may assess deployment parameters and/orfactors affecting deployment to provide a signal or instruction forincreasing the release speed of the cable 125.

In one embodiment, the release rate of the cable 125 is controlled bythe cable handler 160 based on instructions from a controller havingappropriate software that has been programmed based on deploymentparameters and/or factors affecting deployment. For example, informationsuch as vessel speed and spacing between nodes, tensional metrics of thecable 125, among other information, may be inputted and/or monitored toprovide instructions to the controller to vary the rotational speed ofthe cable handler 160.

As described herein, the method described above may be used tofacilitate the placing of nodes 110 on the floor 130 of the water column120. In one embodiment, the powered pinch sheave 211 maintains adeployment rate of the cable 125. The maintained deployment rate maymaintain, cause, or relieve a tensional force in the cable 125. It hasbeen found that varying the tensional force in the cable 125 can createdifferent fall patterns of the nodes 110 and cable 125 through the watercolumn 120.

FIGS. 12, 13 and 14 various embodiments of a fall pattern for nodes 110on a single mainline cable 125B. In the embodiment shown in FIG. 12, areduced tensional force within the cable 125B is maintained. Thetensional force may be monitored and regulated by compensating forfactors that may affect the tensional force. The factors affecting thetension may include, but are not limited to, a rotational speed of thepinch sheave 211, a speed of the vessel 105, a flow current of the watercolumn 120, a wind speed and direction, and a drag of the cable 125B.

In one embodiment, a speed of the vessel 105 and the rotational speed ofthe pinch sheave 211 may be such that the cable 125B is deployed at arate that is between about 1% and 30%, such as about 5% and 20%, fasterthan the speed of the vessel 105. At a deployment rate of about 20%faster than the speed of the vessel 105 a fall pattern 1200 as shown inFIG. 12 may be produced. In another embodiment, the speed of the vessel105 and/or a rotational speed of the pinch sheave 211 may be increasedor decreased to facilitate a deployment rate of the cable 125B to bearound 5% faster than the speed of the vessel 105. At a deployment rateof about 5% faster than the speed of the vessel 105, a fall pattern 1300as shown in FIG. 13 may be produced.

In one embodiment, the deployment rate of the cable 125B may beregulated such that a tensional force of the deployed cable 125B, at atop surface of the body of water 108, may be maintained. The tensionalforce may be maintained between about 1500 Newtons (N) and 3500N, andmore specifically between about 2250N and 2750N. Maintaining a tensionalforce between these limits may produce a fall pattern 1400 as shown inFIG. 14. Further, maintaining the tensional force in the described rangemay help in compensating for factors affecting the placement of thenodes 110, i.e. drift of the nodes 110 away from their intendedlocational placement.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for deploying a plurality of seismic sensor units into a water column, comprising: providing a length of flexible cable from a cable storage device disposed on a vessel to a cable handling device adjacent the cable storage device; routing the cable to pass adjacent a workstation disposed on the vessel; deploying a free end of the cable into the water column while increasing the motion of the vessel to a forward speed; varying the deployment rate of the cable by adjusting a rotational speed of the cable handling device while maintaining the motion of the vessel at the forward speed; and attaching at least one of the plurality of seismic sensor units to the cable as the cable passes the workstation.
 2. The method of claim 1, wherein the deployment rate is greater than the forward speed.
 3. The method of claim 1, wherein the deployment rate is 0 RPM at intermittent intervals.
 4. The method of claim 3, wherein the one or more seismic sensor units are attached during the intermittent intervals.
 5. The method of claim 1, wherein the cable handling device comprises a powered pinch sheave.
 6. The method of claim 5, wherein the rotational speed of the powered pinch sheave is varied between about 0 RPM to about 100 RPM, the powered pinch sheave comprising a diameter of about 32 inches.
 7. The method of claim 6, wherein the forward speed is between about 3 knots to 5 knots.
 8. The method of claim 1, further comprising: discontinuing the rotation of the cable handling device prior to attaching one of the plurality of seismic sensor units to the cable.
 9. The method of claim 8, wherein the rotational speed of the cable handling device is increased after the seismic sensor unit is attached to the cable.
 10. The method of claim 9, wherein the increase in the rotational speed of the cable handling device is initiated by a signal.
 11. A method for deploying a plurality of seismic sensor units into a water column, comprising: providing a cable handling device, coupled to a marine vessel, the cable handling device comprising a powered sheave and an idler sheave, the powered sheave having a first cable contact area and the idler sheave having a second cable contact area opposing the first cable contact area; coupling a length of a flexible cable to the cable handling device in a route to contact the first cable contact area and second cable contact area to maintain a frictional force applied to a section of the flexible cable; routing the cable from the powered sheave to the stern of the vessel to pass across a workstation; deploying a free end of the cable into the water column while increasing the motion of the vessel to a first speed; providing a deployment rate of the cable to a second speed by adjusting the rotational speed of the powered sheave; and attaching at least one of the plurality of seismic sensor units to one of a plurality of attachment points disposed on the cable as the cable passes the workstation.
 12. The method of claim 11, wherein the second speed is varied based on the distance between the attachment points along the length of the cable.
 13. The method of claim 11, wherein the second speed is greater than the first speed.
 14. The method of claim 11, wherein the second speed is 0 RPM at intermittent intervals.
 15. The method of claim 14, wherein the one or more seismic sensor units are attached during the intermittent intervals.
 16. The method of claim 11, wherein the second speed is varied between about 0 RPM to about 100 RPM, the powered sheave comprising a diameter of about 32 inches.
 17. The method of claim 11, wherein the first speed is between about 3 knots to 5 knots.
 18. The method of claim 11, further comprising: discontinuing the second speed to 0 RPM prior to attaching one of the plurality of seismic sensor units to the cable.
 19. The method of claim 18, wherein the second speed is increased after the seismic sensor unit is attached to the cable.
 20. The method of claim 19, wherein the increase in the second speed is initiated by a signal.
 21. A method for deploying a plurality of seismic sensor units into a water column, comprising: providing a length of flexible cable from a cable storage device disposed on a vessel to a powered sheave, the cable having a plurality of spaced apart attachment points; routing the cable from the powered sheave to pass adjacent a workstation disposed on the vessel; deploying a free end of the cable into the water column while increasing the motion of the vessel to a first speed; operating the vessel at the first speed while providing a deployment rate of the cable at a second speed, the second speed being greater than the first speed; decreasing the second speed of the cable as an attachment point approaches the work station; and attaching at least one of the plurality of seismic sensor units to the attachment point at the workstation.
 22. The method of claim 21, further comprising: increasing the second speed of the cable after the seismic sensor unit has been attached to the attachment point.
 23. The method of claim 22, wherein the second speed is increased in response to a signal.
 24. The method of claim 23, wherein in the signal is an auditory or visible signal.
 25. The method of claim 21, wherein the second speed is between about 0 RPM and about 100 RPM, the powered sheave having a diameter of about 32 inches. 